Spheroids are widely used in vitro 3D multicellular model systems that mimic complex physiological microenvironments of tissues. As different cell types vary in deformability and adhesion, the choice of (heterogeneous) cell composition will define overall spheroid mechanics, including their viscoelasticity and effective surface tension. These mechanical parameters directly influence cell sorting and possibly cell invasion into the extracellular matrix. Spheroid models therefore provide fundamental insights in the relation between cellular mechanics and important physiological processes, such as tissue formation, embryonic tissue remodeling, and cancer metastasis. In this review, we first summarize and compare current biophysical tools that probe mechanics of spheroids either from the outside or from within, then relate spheroid mechanics to cell mechanics and cell-cell adhesion, and subsequently discuss the role of spheroid mechanics alongside surrounding microenvironment parameters in (cancer) cell migration. We conclude by pointing out the research gaps and drawing the attention to novel techniques that could shed more light on the biophysical characterization of spheroids in the framework of tissue remodeling and cancer metastasis.@en

Cell spheroids are in vitro multicellular model systems that mimic the crowded micro-environment of biological tissues. Their mechanical characterization can provide valuable insights in how single-cell mechanics and cell-cell interactions control tissue mechanics and self-organization. However, most measurement techniques are limited to probing one spheroid at a time, require specialized equipment and are difficult to handle. Here, we developed a microfluidic chip that follows the concept of glass capillary micropipette aspiration in order to quantify the viscoelastic behavior of spheroids in an easy-to-handle, more high-throughput manner. Spheroids are loaded in parallel pockets via a gentle flow, after which spheroid tongues are aspirated into adjacent aspiration channels using hydrostatic pressure. After each experiment, the spheroids are easily removed from the chip by reversing the pressure and new spheroids can be injected. The presence of multiple pockets with a uniform aspiration pressure, combined with the ease to conduct successive experiments, allows for a high throughput of tens of spheroids per day. We demonstrate that the chip provides accurate deformation data when working at different aspiration pressures. Lastly, we measure the viscoelastic properties of spheroids made of different cell lines and show how these are consistent with previous studies using established experimental techniques. In summary, our chip provides a high-throughput way to measure the viscoelastic deformation behavior of cell spheroids, in order to mechanophenotype different tissue types and examine the link between cell-intrinsic properties and overall tissue behavior.@en